The spinal column is a highly complex system of bones (i.e., vertebral bodies) and connective tissues that provides support for the body and protects the delicate spinal cord and nerves. The spinal column includes a series of vertebrae stacked one atop the other, each vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. Situated between each vertebral body is an intervertebral disc that cushions and dampens compressive forces on the spinal column. A vertebral canal containing the spinal cord and nerves is located within the forward-facing surface of the vertebral bodies.
There are many types of spinal column disorders. Patients that suffer from such disorders typically experience extreme and debilitating pain, as well as diminished nerve function. Examples of such spinal column disorders include, but are not limited to, scoliosis (i.e., abnormal lateral curvature of the spine), kyphosis (i.e., abnormal forward curvature usually in the thoracic portion of the spine), excess lordosis (i.e., abnormal backward curvature usually in the lumbar portion of the spine), spondylolisthesis (forward displacement of one vertebrae over another usually in the lumbar portion or cervical portion of the spine), etc. There are still other types of spinal column disorders caused by physiological abnormalities, disease and/or trauma such as, for example, ruptured or slipped discs, degenerative disc disease, fractured vertebra, and the like.
Multi-segmental spinal fixation is an accepted surgical procedure in the treatment of such spinal column disorders. It involves the use of a series of pedicle screw assemblies and one or more spine rods. The pedicle screw assemblies each include a screw that is threadedly screwed into one of a plurality of adjacent vertebral bodies. A spine rod (contoured or straight) is fixedly secured to a spine rod clamping body of each one of the pedicle screws for fixing two or more adjacent vertebral bodies in a static relative position. In this manner, spinal fixation can be used to alter the alignment of adjacent vertebrae relative to one another so as to change the overall alignment of the spine, to preclude relative movement between adjacent vertebrae, and the like.
Rigid fixation resulting from pedicle screw assemblies and attached spine rods that inhibit flexure within the spine rod clamping body, the spine rod and interface therebetween can result in stresses that are placed on the fixation system and attached bone structure after implantation of the fixation system such as, for example, resulting from normal activity of the patient. These stresses can adversely impact several aspects of the bone fusion process. In particular, these stresses can adversely impact a rate at which such bone fusion progresses and can result in damage to the interface between the bone screw and bone from overstressing of such bone-to-screw interface prior to such bone fusion progressing to a sufficient level.
Therefore, a pedicle screw assembly having a spine rod clamping body that exhibits a limited amount of elastic deformation at a region location between its spine rod mounting portion and its bone screw connecting portion would be advantageous, desirable and useful.